Method of preparing lead alloys



Dec. 27, 1955 NEHER METHOD OF PREPARING LEAD ALLOYS 2 Sheets-Sheet 1Filed Feb. 29, 1952 m \Q k E mm mm mm vw km mm INVENTOR.

CLARE EM. IVE HER B WW Y TTOR/VEY Dec. 27, 1955 c. M. NEHER 7 2, 8,

METHOD OF PREPARING LEAD ALLOYS FiledFeb. 29, 1952 2 Sheets-Sheet 2 fI85 190 195 200 205 M/Luvou's IN VENTOR.

CLARE E .NE'HER A T TOR/V5 Y United States Patent METHOD OF PREPARINGLEAD ALLUYS Clarence M. Neher, Baton Rouge, La., assignor to EthylCorporation, New York, N. Y., a corporation of Delaware ApplicationFebruary 29, 1252, Serial No. 274,233

3 Claims. (Cl. 75-467) This invention relates to the manufacture ofreactive alloys of lead. More particularly the invention relates to anew and improved process for combining lead with at least one additionalalloy component such as, for example, an alkali metal or an alkalineearth metal.

The alloys of lead with other metals find usage for various purposes. Asexamples of the lead alloys finding wide commercial usage may bementioned solder, type metal, pewter and alloys of lead with the alkalimetals or alkaline earth metals. The latter alloys, including, forexample the alloys of lead with sodium, potassium, magnesium, calcium,lithium, find extensive usage as chemical reactants, particularly in themanufacture of organic compounds of lead, such as tetraethyllead. Thealloys used for such purposes may be binary alloys, or may contain morethan one alkali or alkaline earth metal component, or an alkali metaland an alkaline earth metal. The preparation of such alloys hasheretofore been quite awkward. It has been considered essential inpreparing such alloys, to thoroughly mix large batches, then analyze,and then to make further appropriate additions to correct thecomposition as required, then to remix, and reanalyze. The drawbacks ofsuch a procedure are obvious. Further, in mixing the lead and addedcomponents, appreciable amounts of heat are frequently generated. Forexample, in mixing sodium and lead in proportion to provide monosodiumlead alloy, sufficient heat is generated to raise the temperature asmuch as 800 F. Accordingly, it has been necessary to mix the componentsof the alloy slowly so as to avoid breakage of the manufacturing potsbecause of the thermal effects accompanying the process. The priormethods, then, have been limited in efiiciency owing to the apparentnecessity of blending large batches of alloy, and further by the factthat the characteristics of the system restrict the rapidity with whichsuch batches can be prepared. Some of these difficulties in the priorart are illustrated by Fisher et al. U. S. Patent No. 2,276,031, whichshows the complications involved in one type of prior art preparation,as well as the Amick et a1. Patent No. 2,043,224, which illustrates thecomplicated apparatus heretofore considered necessary. The preparationof reactive lead alloys has been further complicated by the necessity ofkeeping the metals being processed, and samples thereof, at all timesunder inert conditions.

Among the objects of the present invention is the provision of a processfor preparing alloys of lead with other metals, which process avoids theabove and related disadvantages. A further object is to provide a highcapacity process wherein a highly uniform composition is attained butnevertheless only a minor quantity of material is processed or mixed atany one time. Another object is to provide a continuous process havingan effective method of flow control and proportioning. The control andproportioning is responsive to the composition of the alloy concurrentlyproduced, so that alteration or error allows immediate adjustment. Stillanother object is to provide a process particularly effective inpreparing the reactive 2,728,656 Patented Dec. 27, 1,955

2 alloys of lead, in that alloying to a desired composition is effectedwithout exposure of the metal components. Additional objects will appearhereafter.

The present process attains the above objects and provides as welladditional advantages over prior methods. The process and the details ofoperation, and of suitable equipment will be more readily understoodfrom the description below, and by reference to the accompanyingfigures. Figure 1 is a schematic showing of an apparatus suitable for apreferred embodiment of the process wherein automatic operation isprovided. Figure 2 presents a curve of a typical voltage versuscomposition relationship such as is employed in the process.

It has been discovered that the alloys oflead can be readilymanufacturedby feeding together molten streams of the lead, or if desired, apredominantly lead alloy, and then the alloying metal, then mixing, therelative proportions of the components being controlled in accordanceWith a potential or voltage difference existent between the so-formedmolten alloy and a molten reference metal at the same temperature as thealloy. A feature of the process is that at all times the composition ofthe alloy produced is immediately ascertained thereby allowing controlof the feed proportions to provide a uniform composition.

In most forms of the process, the formation of the alloy is accompaniedby the liberation of heat of reaction, and a cooling step isincorporated to reduce the temperature of the mixed alloy to a uniformtemperature, above the freezing point of the alloy. Such a uniformtemperature assures obtaining the full benefits of the process. In thepreferred embodiments of the invention, the mixing and coolingoperations are carried out concurrently. 7

Process flows and arrangement of suitable apparatus are illustrated byFigure l, for a preferred embodiment of the process wherein automaticproportioning of the alloy components is achieved. For simplification,the following description is given for application to the manufacture ofa lead-sodium alloy, although the process is also fully applicable toother lead alloys.

Referring to Figure l, the apparatus shown includes a sodium feed tank10, fed or charged as desired through a valved sodium feed line 14. Alead feed pot 12 is similarly charged as necessary with molten lead fedthrough a valved feed line 13.

feeds to the mixing operation. The flows of the sodium and lead arecontrolled by appropriate control valves 28 in the sodium transfer line,and 30 in the lead transfer line.

The sodium-is fed to the jacket tube 24 of a concentric tube feeder tothe heat exchanger-mixer 32. The lead transfer line 22 is continued, asthe center tube of the concentric tube feeder, into a mixing tube 26 inthe heat exchanger-mixer 32. The concentric tube feeder 24 prevents thesodium and lead from contacting each other until within the heat removalzone. The heat exchangermixer, in addition to controlling the dischargetemperature of the mixed alloy by removal of the heat of mixing, alsoassures uniform mixing of the sodium and lead by the internal turbulencegenerated by the flow of the liquid metal and the mixing currentsgenerated by the heat of reaction.

The temperature of the alloy discharged by the heat exchanger-mixer isascertained by a thermocouple element 34 inserted in the alloy line 56.The temperature is maintained constant by appropriate control of theflow of a coolant liquid to the jacket of the heat exchanger-mixer 32.Immediately following the thermocouple 34 the alloy flows through achamber or cell 36 wherein the voltage of the alloy as ascertained withrespect to that of a reference metal. It has been found that thisvoltage or E. M. F. difference provides an accurate guide or ameasurement of the composition of the alloy.

The voltage as ascertained in the cell 36 is transmitted to aninstrument 60 by electrical leads 59. The instru ment 60 may suitablyprovide a continuous record of the voltage, expressed directly in termsof the alloy composition if desired. Incorporated in the instrument isan amplifier or convertor which is of conventional design. The amplifiertranslates the voltage impulses received from the cell 36 to controlforces, either pneumatic or electrical, for example, which aretransmitted by line 57 and provide control of the setting of the controlvalve 28 by motor 58.

In operation, the flow of lead from the lead supply pot 12 is usuallyset at a constant value by setting the lead control valve 30. The sodiumflow is maintained at the desired rate by the control valve 28 which isactuated as above described. Any change in setting of valve 28 is thenin response to variations in the voltage of the alloy as measured incell 36.

Following passage through the cell 36 the alloy flows through a conduit56 and is delivered to a holdup pot 38. A supply of several hoursproduction is maintained in the holdup pot 38, and continuous agitationof the product therein is provided by an agitator 40. Alloy istransferred to subsequent consuming operations through transfer line 42by means of centrifugal pump and drive 55.

The heat exchanger 32 may be any of a variety of types, the most usualbeing to provide a jacket for a coolant around the mixing tube 26. Acoolant is passed through the jacket, the coolant preferably being amaterial which is stable at the high operation temperatures required. Asuitable coolant is the eutectic mixture of diphenyl and diphenyl-oxide.The coolant is fed countercurrently to the flow of the alloy in the heatexchanger-mixer, being introduced through a supply line and dischargedby an outflow line 74. A coil 76 forms part of the coolant outflow line74. A water spray, fed through a line 78, is sprayed over the coil 76 bya spray head 75, and provides for maintaining a uniform temperature ofthe coolant supply in the coolant tank 70. Customarily and preferably,the coolant supply temperature is held constant at a temperatureslightly above the freezing point of the alloy being manufactured. Thisassures that the alloy will not be frozen in the heat exchanger-mixerunit. Coolant is discharged by pump 77 through a line 72 to the heatexchanger-mixer, the rate of fiow being controlled by valve 80. Thecontrol valve 80 is set by the operating motor thereof, which isactuated by electrical or pneumatic impulses from the conventionaltransmitter 61. The transmitter 61 may also incorporate a recorder forproviding a chart of the alloy temperatureas determined by thermocouple34.

It is highly desirable that means as above described, or equivalentmeans known in the process industries, be provided for assuring aconstant temperature of the alloy discharged from the heatexchanger-mixer. This condition is desired because in addition tovarying with the composition of the alloy, the voltage differenceascertained by cell element 36 varies somewhat with temperature. Howeverin some few instances, when only a minor quantity of alkali metal is tobe incorporated in the alloy, for example, temperature adjustment is notessential.

The cell or voltage detector 36 may assume several forms. In everyinstance, however, provision must be made for measurement of voltagedifference which is truly representative of that between the alloy beingproduced and the reference metal. To accomplish this result, provisionis necessarily made for isolating the reference metal from the surfaceof the body of the alloy, but within the mass of the alloy product. Asuitable apparatus providing this isolation comprises a glass capsule ortube, holding the reference metal within the mass of alloy. A secondglass envelope surrounds and is spaced apart from this tube at the alloysurface and provides electrical insulation of the surface thereof fromthe main tube. A two wire lead line 59 includes a probe or wire from thereference metal plus a wire from the alloy itself, and relays thevoltage difference to the instrument 60. The glass of this capsule orenvelope is necessarily of a composition permissive of migration orpermeation therethrough of ions of the alloy component beingascertained. Thus a low sodium boro-silicate glass, besides beingresistant to thermal shock, is permeable to sodium ions. Whendetermining the concentration of other alloy components, for example,magnesium, it is desirable that the glass or barrier material containsome magnesium present in its composition, in order to provide a spatialconfiguration facilitating or permitting permeation of magnesium ions soas to permit measurement of a voltage difference.

A typical voltage-composition relationship as employed in an embodimentof the process is illustrated by Figure 2. The figure is a plot of'therelationship of the voltage difference between a molten alloy consistingof sodium and lead, and pure sodium. The chart shows suchvoltage-composition relationships at temperatures of 440 C. and 450 C.It will be noted that with an increase in sodium content, the voltagedifference decreases. Thus, at 440 C., at a sodium content of 9.75weight percent, the voltage is 202.6 millivolts, and at exactly 10weight percent sodium, the voltage is 197 millivolts. This relationshipthus provides an almost instantaneous method of ascertaining thecomposition of the alloy produced.

If desired, the manufacturing operation may be manually controlled.Thus, referring to the flow diagram of Figure 1, the sodium controlvalve may be manually adjusted in response to any changes in the voltagedifferences as determined by cell 34. Manual control is, however,ordinarily preferred only for standby or emergency operation, because ofthe high degree of uniformity readily attained by automatic means.

The holdup pot 38, while primarily intended as a product reservoir, alsoserves an additional function in minimizing variation of alloy deliveredto subsequent consuming operations. Thus, even if a temporary unbalancein the flow rate of one of the alloy components results in production ofalloy deviating from the desired composition, this effect is minimizedby the dilution effect of the alloy in the holdup pot. In addition, theholdup pot provides storage capacity when either the alloy consumingoperation is interrupted, or when operation of the alloy manufacturingunit is temporarily suspended.

As a working example of the production of monosodium lead alloy, NaPb,liquid lead is fed through the lead transfer line at a rate of about8100 pounds per hour and at a temperature of about 450 C. Liquid sodiumis fed through the sodium transfer line 20 at a rate of about 900 poundsper hour, the flow rate being controlled by regulating valve 28. The twometal streams are fed, through the feed section 24 to the cooling-mixingtube 26 in the heat-exchanger-mixer. In passing therethrough, thetemperature of the metals rises, owing to the heat of mixing, but isagain reduced to 450 C. before discharge. The alloy then is passedthrough the voltage determination cell 36, wherein the voltage withreference to pure sodium is measured. The voltage difference signal istransmitted to the recording-transmitting instrument 60, which in turncontrols the setting of the sodium control valve 28 in response to anyvoltage difference deviation, to maintain a constant value of 196millivolts. The manwrrfi i ufactured alloy then passes to the holdup pot38, which normally contains about four hours production, but hascapacity for approximately twice that quantity.

The process is capable of valuable usage for numerous embodiments inaddition to the above manufacture of monosodium lead alloy. Alloys ofappreciably lower or higher sodium content can be made, and in addition,the method is easily utilized in making ternary alloys. Thus, forexample, if the preparation of an alloy containing percent sodium, 1percent potassium, and 89 percent lead is desired, the lead and sodiumare first blended. Potassium is then alloyed with the liquid sodium-leadalloy, the voltage difference between the final alloy and pure sodiumagain being employed as a guide or control point.

As indicated above, it is not essential that the reference metalemployed be identical in composition to the alloying metal or metalsbeing incorporated into the lead. As mentioned above, for example, whenalloying potassium metal, the reference metal can be pure sodium andaccurate results will be obtained. Therefore, it is possible to utilizea reference metal consisting of a low melting mixture containing as acomponent the alloying metal being determined. Thus, for example, indetermining the amount of calcium in an alloy of lead and calcium,sodium saturated with calcium may be used as the reference metalmixture.

For simplicity, the apparatus illustrated by Figure 1 omits featuresusually found in processing reactive metals, which Will be readilyapparent to those expert in the field. Thus, provision is made forminimizing exposure of the feed metals, or the product alloy, tomoisture or active atmospheres. For example, a blanket or atmosphere ofany pure inert gas is maintained over the metal components in tanks orvessels. Another frequently used feature is means to supply heat to thestorage tanks and to the holdup pot. Normally such pots will be providedwith efiicient insulation, but even under such conditions, some heatwill occasionally be required to prevent freezeup.

The embodiment described above with reference to Figure 1 involves theconcurrent mixing of the alloy components and the removal of reactionheat accompanying the mixing. This concurrent operation is highlydesirable as it utilizes the natural turbulence of flow, and the turbulence generated by the heat effects of alloy formation, to secureintimate dispersion of the alloy components one within the other.Although advantageous, this concurrent operation is not essential toobtain the major benefits of the process. If desired, the mixing can becarried out separately. This is done, for example, by feeding the sodiumand lead streams to a small agitated vessel. Here, these componentscould be intimately mixed by mechanical stirring resulting inappreciable heating of the alloy. The mixed alloy is then passed througha heat exchanger for cooling to the desired control temperature. Theadvantage of this mode of operation is that the efliciency of the mixingstep is rendered independent of the production rate, which is sometimesa factor in the embodiment illustrated by Figure 1.

As many modifications of the process will be evident in addition to thespecific description and examples given herein, it will be understoodthe process is not limited except as by the claims below.

What is claimed is:

1. A process for continuously manufacturing a molten alloy of lead andat least one alkali metal comprising providing a stream comprisingmolten lead, and a stream of molten alkali metal, the flow of one ofsaid streams being controlled by means responsive to a voltagedifference, combining the lead and alkali metal streams as an additionalcombined stream and mixing the lead and the alkali metals in thecombined stream and concurrently with the mixing removing the heatgenerated and cooling to a constant temperature, above the melting pointof the alloy desired, then passing said combined stream past a referencemetal specimen, comprising an alkali metal corresponding to a componentof the alloy, the specimen being isolated from the periphery of thecombined stream, and separated from the combined stream by a membranepermeable to ions of the reference metal, whereby a voltage ditferenceis developed between the combined alloy stream and the reference metal,and transmitting the voltage dilference to the means for controlling theflow of one of said streams.

2. The continuous process for manufacturing a molten alloy of sodium andlead of substantially constant composition comprising providing a streamof molten lead at a substantially constant rate, providing a stream ofmolten sodium at a rate controlled by means responsive to a voltagedifference developed as hereafter defined, feeding together the leadstream and the sodium stream and mixing said streams by flow. throughan, extended flow channel and concurrently removing heat developed inthe mixing and cooling to a constant temperature, above the meltingpoint of the desired alloy, then passing the mixed stream past a sodiummetal specimen, the specimen being isolated from any boundary of themixed stream and being separated from the mixed stream by a membranepermeable to sodium ions at the said temperature, whereby a voltagedifference is developed between the mixed stream and the sodiumspecimen, and transmitting the voltage difierence to the means forcontrolling the flow of the sodium stream.

3. The continuous process for manufacturing a molten alloy of sodium,potassium and lead comprising providing a stream of molten lead at asubstantially constant rate, providing a stream of molten sodium at arate controlled by a first means responsive to a voltage differencedeveloped as hereafter defined, feeding together the lead stream and thesodium stream and mixing said streams by flow through an extended flowchannel and concurrently with the mixing removing heat developed in themixing and cooling to a constant temperature above the melting point ofthe mixed stream, then passing the mixed stream past a first sodiummetal specimen, the specimen being isolated from any surface of themixed stream and being separated from the mixed stream by a membranepermeable to sodium ions, whereby a first voltage difierence isdeveloped between the mixed stream and the first sodium specimen, andtransmitting the first voltage difference to the first means, forcontrolling the flow of the sodium stream, providing a stream of moltenpotassium at a rate controlled by a second means responsive to a voltagedifference developed as hereafter defined, feeding together the mixedstream and the potassium stream and mixing said streams by flow throughan extended flow channel, and concurrently with the mixing removing heatdeveloped in the mixing and cooling to a constant temperature, above themelting point of the desired alloy, then passing the so mixed alloystream past a second sodium metal speci men, the specimen being isolatedfrom any surface of the alloy stream and separated from the alloy streamby a membrane permeable to sodium ions, whereby a second voltagedifference is developed, between the alloy stream and the second sodiumspecimen, and transmitting the second voltage difference to the secondmeans for controlling the flow of the potassium stream.

References Cited in the file of this patent UNITED STATES PATENTS1,450,023 Edelman Mar. 27, 1923 2,091,801 Amick et al. Aug. 31, 19372,565,121 Clardy et a1 Aug. 21, 1951 2,621,671 Eckfeldt Dec. 16, 1952FOREIGN PATENTS 741,982 Germany Nov, 19, 1943

1. A PROCESS FOR CONTINUOUSLY MANUFACTURING A MOLTEN ALLOY OF LEAD ANDAT LEAST ONE ALKALI METAL COMPRISING PROVIDING A STREAM COMPRISINGMOLTEN LEAD, AND A STREAM OF MOLTEN ALKALI METAL, THE FLOW OF ONE OFSAID STREAMS BEING CONTROLLED BY MEANS RESPONSIVE TO A VOLTAGEDIFFERENCE, COMBINING THE LEAD AND ALKALI METAL STREAMS AS AN ADDITIONALCOMBINED STREAM AND MIXING THE LEAD AND THE ALKALI METALS IN THECOMBINED STREAM AND CONCURRENTLY WITH THE MIXING REMOVING THE HEATGENERATED AND COOLING TO A CONSTANT TEMPERATURE, ABOVE THE MELTING POINTOF THE ALLOY DESIRED, THEN PASSING SAID COMBINED STREAM PAST A REFERENCEMETAL SPECIMEN, COMPRISING AN ALKALI METAL CORRESPONDING TO A COMPONENTOF THE ALLOY, THE SPECIMEN BEING ISOLATED FROM THE PERIPHERY OF THECOMBINED STREAM, AND SEPARATED FROM THE COMBINED STREAM BY A MEMBRANEPERMEABLE TO IONS OF THE REFERENCE METAL, WHEREBY A VOLTAGE DIFFERENCEIS DEVELOPED BETWEEN THE COMBINED ALLOY STREAM AND THE REFERENCE METAL,AND TRANSMITTING THE VOLTAGE DIFFERENCE TO THE MEANS FOR CONTROLLING THEFLOW OF ONE OF SAID STREAMS.